Hans R. von Gunten

Infiltration of inorganic compounds from the Glatt River, Switzerland, into a groundwater aquifer

The behavior of dissolved (<0.45 μm) inorganic compounds during infiltration of river water into the adjacent aquifer (unconsolidated glacio-fluvial sediments) was investigated at the Glatt River, Switzerland, field site. The water was sampled in the river and from wells at distances of 2.5, 5, 13, and 110 m along an estimated groundwater flow line. Sodium, K, Ca, Mg, Sr, Cr, Cu, Zn, Cd, Pb, Cl−, NO3−, SO42−, and PO43− were measured using AAS, NAA, and ion chromatography. Groundwater concentrations of these species are mainly determined by the concentrations in the river. However, the concentrations of NO3−, (PO43−), Cr, Cu, Zn, Cd, and Pb are also subject to seasonal variations in the near infiltration field (≤ 5 m). These variations are probably triggered by temperature dependent biological processes which influence parameters such as pH, redox potential and complexing agents. The redox potential controls the chemical behavior of Mn, which influences the solubility of heavy metal compounds. The extent of inorganic pollution in the investigated system is still much below drinking water standards, but for Cd, reaches the toxicity limit for aquatic organisms.

Uranium infiltration from a river to shallow groundwater

The infiltration of uranium from the polluted River Glatt (Switzerland) into a hydraulically connected saturated aquifer was investigated during a period of almost five years. The uranium concentrations and the 234U238U activity ratios (ARs) were analysed monthly in the water of the river and of four groundwater sampling wells. The speciation of uranium and its relation to other aqueous and solid components were investigated experimentally and in model calculations. The uranium concentration and the ARs in the river varied seasonally with a maximum and a minimum, respectively, in summer. Processes, such as photo-reductive dissolution of iron-oxyhydroxides or the enhanced decomposition of organic matter and calcite in the upstream, eutrophic Lake Greifen may have caused these variations. Laboratory experiments confirmed a possible release of uranium by photochemical reactions. The concentration maximum of uranium was also detected in the shallow groundwater, but with a delay of about six months to the maximum in the river. Under the assumption that the maxima in the river and the groundwater were related, an in situ distribution coefficient (KD) for uranium of ≈7 mL g−1 can be calculated for this Quaternary gravel aquifer. Uranium was present predominantly as UO2-carbonate complexes, whereas the formation of phosphate and organic complexes (e.g., UO2-humates/EDTA/NTA) was negligible. Particles and colloids played a minor role for the transport of uranium in this aquifer. In the course of this study, we observed an ongoing general decrease of the uranium concentrations and a disappearance of its summerly maxima in the River Glatt. We relate this unexpected effect to a better control of the phosphate concentration in surface waters, which diminished the growth of aquatic biota. This, in turn, led to changes in the redox conditions of lake and river sediments, and herewith to a reduced release of heavy metals, including uranium. The results of this case study can be applied to estimate the migration behavior of other actinide oxyions (e.g., PuO22+NpO2+) in shallow heterogeneous aquifers, which abound in alpine and pre-alpine locations.

The reactor accident at chernobyl: A possibility to test colloid-controlled transport of radionuclides in a shallow aquifer

Radioactive fall-out from the damaged nuclear power station at Chernobyl (USSR) has been measured in May 1986 in the River Glatt (Zurich, Switzerland) and in a shallow groundwater stream. This aquifer is hydraulically connected to the river and recharged by river water. Ruthenium-103, I-131, Te-132, Cs-134 and Cs-137 were measured several times using gamma-ray spectroscopy. By filtration through 0.45 μm, 0.2 μm and 0.05 μm filters the radionuclides were partitioned between solution (filtrate < 0.05 μm) and particles/colloids. In the river, the main radioactivity for all the investigated nuclides was found in the water passing the 0.05 μm filter. Among the particulates the highest radioactivity was detected in the fraction > 0.45 μm, the two smaller sizes contributing only little. In the water infiltrating into the groundwater Ru-103, I-131 and Te-132 were found almost exclusively in the filtrate ( 0.05 μm suggesting their retention by the heterogeneous glaciofluvial outwash deposits (stones, gravel, sand, clays).

Colloid-related infiltration of trace metals from a river to shallow groundwater

Abstract The role of colloids for the transport of the trace metals Al, Cd, Cu, Fe, Mn and Zn was investigated in the River Glatt and in a groundwater infiltration zone near Glattfelden, Switzerland. Ultrafiltration techniques were applied to fractionate colloids in the size range 2–450 nm. From the analysis of the above elements, Si and total organic carbon, it was concluded that colloids play a minor role for the transport of trace metals in the river and from the river into the adjacent heterogeneous aquifer. Colloids in the river and in the aquifer show a different element distribution. It was furthermore demonstrated that filtration through 450-nm filters is in general a method adequate for the separation of solids and liquids in natural water systems. The results of this case study may be applied to other shallow heterogeneous aquifers with interstitial porosity. Extended aquifers of this composition are mainly found in Alpine and peri-Alpine locations, but also elsewhere.

DISTRIBUTION OF URANIUM- AND THORIUM SERIES RADIONUCLIDES IN MINERAL PHASES OF A WEATHERED LATERITIC TRANSECT OF A URANIUM ORE BODY

Abstract A surficial, weathered 400 m long profile of the Ranger One ore body #3 (Northern Territory, Australia) has been characterised to a depth of 10 m in terms of the total uranium, 238 U , 234 U , 232 Th , 230 Th and 228 Th distributions, and measurements of other geochemically important elements. The characterisation was limited to the 234 U , 230 Th and 228 Th , precipitation due to evaporation of ground- and interstitial water, and the adsorption of uranium and thorium within a time frame less than that required for 234 U / 238 U and 230 Th / 234 U to achieve secular radioactive equilibrium. The mineralogical composition of the soil is to some extent responsible for local variations in the measured properties. The differences in chemical speciation and behaviour of uranium and thorium enhance the variability in the 230 Th / 234 U activity ratios. The monsoonal climatic and hydrological variations intensify some of the observed effect.

NEWFIT, a computer program for the analysis of alpha, X-ray and gamma-ray spectra

Abstract The computer program NEWFIT has been developed for analysis of gamma-ray, X-ray and alpha spectra. The general shape used for the analysis of activity peaks is a Gaussian function. An exponential tail can be added for use in alpha spectra analysis. The algorithms to analyze the peak shapes and the program operation are presented. Special features include the ability to create realistic peak shapes based on the systematic deviations of the real peaks from the theoretical Gaussian shape, as well as the option to constrain the calculated areas of peaks from a given alpha emitting nuclide to their relative branching ratios. The program is available from the authors.

Chemical Sample Preparation for the Determination of Silicon-32 by Accelerator Mass-Spectrometry

Silicon-32 is produced in very small concentrations by interactions of cosmic rays in the atmosphere. It can be used for nuclear dating purposes, but its measurement is very difficult. The recent availability of accelerator mass-spectrometry (AMS) may help to increase the sensitivity for detection of Si. We describe a chemical method which produces elemental silicon to be used in the ion source of an AMS-installation. The material containing Si is dissolved in HF. SiF4 is reduced to SiH4 which is thermally decomposed to elemental silicon. Elemental silicon, deposited on graphite discs, is, thus far, the most suitable material for Si determinations by AMS, yielding the purest and highest ion currents of all tested materials. At present we can determine Si/Silol ratios of about 10 and reach the same sensitivity as in radiochemical counting techniques.

The decay of 251Bk

Abstract The decay of 251 Bk has been studied by radiochemical techniques. The half-life of 55.6 ± 1.1 min agrees with the literature. Relative intensities of γ-rays, including previously unknown γ-rays at 129.9 keV and 163.8 keV, have been determined. The estimated absolute intensity of the γ-ray at 177.7 keV is (5.2 ± 0.6)%. The maximum β-energy has been measured to be 915 ± 10 keV and was used to determine the mass of 251 Bk. A decay scheme based on these measurements is given.